Method of purifying and stabilizing



Patented Mar. 10, 1936 STATES PATENT FFICE METHOD OF PURIFYING AND STABILIZING AROMATIC LIGHT OIL Alfred Pott, Hans Broche, and Kuno Ehrmann, Essen, Ruhr, Germany 4 Claims.

This invention relates to a process for purifying liquid fuel obtained in the high temperature coking of mineral coals and forming a light oil which boils up to 180 to 200 C. It is known that such light oil consists entirely of hydrocarbons both in a saturated and unsaturated form. Such light oils develop, if used as motor fuel, more heat than fuels obtained from petroleum-oils and distillates which consist of entirely difierent hydro-carbons, namely, those of the aliphatic class and of naphthenes.

The problem which arises in the purification of these fuels is the obtaining in maximum possible yield of products which burn satisfactorily in the engine and which, more particularly, do not give rise to resinification. The said fuels are completely utilizable, either alone or in admixture with other fuels, and are even advantageous since they prevent so-called engine knock. It is necessary, however, to remove the impurities from these fuels which are present in the form of resins or which form resins during storage. A practical purification process, therefore, which answers the said requirements must selectively remove only the resins and resin producers from the fuels without substantially attacking the latter.

Up to now a wash with concentrated sulphuric acid has been employed for purifying motor fuel consisting in light oils of aromatic character.

Various efforts have been made to carry out the sulphuric acid treatment in such a way that only the resin producers are removed from the aromatic light oil, the unsaturated hydrocarbons remaining in the oil with the result that large yields of motor oil which is highly valuable and stable on storage would be obtained. None of these attempts, however, led to the desired result. More particularly, these unsuccessful attempts proposed to use simply a more dilute sulphuric acid in place of the concentrated sulphuric acid previously employed and, corresponding to the former method of working, then to wash the product washed with diluted acid with some cold water and thereupon to neutralize with alkali in the cold. Such a motor oil treated with dilute acid and neutralized in the usual manner formed resins on storing and consequently did not conform to the requirements which must be imposed on a highly valuable motor oil. The result, moreover, was no better when the treatment with diluted acid was carried out at elevated temperature up to the boiling point of the oils under treatment. When a motor oil free from resin producers was obtained by such treatment with diluted acid at suitably high temperatures, the attack of the washing acid was so intensive that the Valuable unsaturated aromatic hydrocarbons were destroyed thereby, and almost the same high washing losses were obtainedas in the case of washing with ,concentrated sulphuric acid.

According to the present invention the maximum yields of highly valuable motor aromatic light oil which are stable on storage and free from resin producers, are produced, with minimum washing losses during the sulphuric acid wash, by washing the raw aromatic light oil obtained by high temperature coking of mineral coals with small quantities of diluted sulfuric acid of only approximately B. concentration, i. e, containing approximately 77% sulphuric acid, at ordinary or slightly raised temperatures, and then treating the washed products with al kali in the heat,

7 The reason for the surprising success of the process may, amongst other things, lie in the following: in the treatment with diluted acid of aromatic hydrocarbon mixtures containing more or less large quantities of unsaturated aromatic hydrocarbons, certain quantities of sulphonic acids and more particularly esters thereof are formed. These substances were directly further polymerized to resins in the washing with concentrated acid previously employed. By treating the raw aromatic light oil with diluted acid the polymerization of the said sulphonic acids and esters thereof does not occur. These esters are not destroyed by the heretofore usual neutralization of the washed aromatic light oil with alkali, carried out in the cold; they have the peculiarity, however, not only of themselves gradually polymerizing to resins, particularly by access of air during storage, but they also act as it were catalytically on the unsaturated aromatic hydrocarbons which remain in the aromatic light oil after the said treatment with diluted sulphuric acid. Whereas these unsaturated aromatic hydrocarbons are themselves quite stable on storage and form no resins, they polymerize with great avidity as soon as the sulphonic acids, esters thereof, and so forth which arise during the treating of aromatic light. oil with diluted acid are present. Herein is to be seen the reason for the former lack of success in the treatment with diluted acid, in which the washed product was merely neutralized with alkali in the cold in the usual manner. The former treated product contained sulphonic acid esters and the like compounds in considerable quantiing the subsequent distillation.

ties which, as resin producers, obviously make the aromatic light oil useless. Only the new process provided by this invention, i. e. washing the crude aromatic light oil with diluted sulphuric acid and then treating with hot alkali,

enables the purification to be carried out with extremely small washing losses and yet perfectly satisfactory aromatic light oil, of high value from the driving point of view, to be obtained in maximum yields.

The hot treatment with alkali of the product washed with diluted sulphuric acid which is provided by the invention, enables, for the first time, motor aromatic light oil which is not yet stable on storage after the acid wash to be stabilized.

The invention can be carried out in various ways. The treatment of the raw products with diluted sulphuric acid is preferably effected at the usual temperatures, more particularly at temperatures between 20-40 C. If the exterior temperatures are very low, or if, depending on the quality of the raw products, there are only very small heats of reaction, then it is frequently advisable moderately to heat the product during the washing with diluted acid to temperatures up to about 40 C., since at too low temperatures stiff or solid resins can readily form. After treatment with the diluted acid the product can be neutralized in the cold so that the acid residues still present do not adversely affect the stills dur- The treatment with hot alkali of e. g..100 C. or over can, for example, be carried out in such a way that a certain quantity of caustic soda or the like is introduced into the still and the product distilled off inpresence ofthe caustic soda. However, the vapours from the aromatic light oil may also be led through hot caustic soda, and the destruction of the sulphonic acid esters and the other resin producers brought about in this way. Finally, both methods may be used in order to destroy, both the volatile esters and the esters remaining in the residue.

In the purification of light, oil, obtained by coking mineral coals, operations may, for example, be carried out by first of all preliminarily washing the light oil with about 1% sulphuric acid of about 60 B. in order to dry the light oil and to remove the bases, then washing with about 3% sulphuric acid of about60 B., i. e.of ap-. proximately 77% acid and, after withdrawing the washing acid and the resins formed, after washing withabout 1% caustic soda. The product treated thus is now filled into the still with an addition of about 1% of caustic soda in a concentration of 18%, and then distilled to the pure. marketable product in a suitable manner, first of all by means of indirect steam and then with direct steam. The final treatment with alkali at elevated temperature, however, can also advantageously be carried out at the boiling temperature of the oils, uniformly above 100 0. therefore, in such a way that the product treated with diluted acid, preferably after neutralization in the cold, is distilled, if necessary or desired over alkali, and the vapours led through hot caustic soda. It is sometimes observed that aromatic light oils, mildly purified in the manner described obtain a yellow colour. In order to avoid this yellowing it has been found advisable to effect a treatment with sufiicient quantities of hot Water directly after the treatment with diluted sulphuric acid, before the aromatic hydrocarbons come into contact with alkali. It could be established that in the yellowvcoloured hydrocarbons free bases, such as, for example, pyridine, quincline, and the like, are present, since it may be that in the aromatic hydrocarbons purified with acid pyridine sulphate and the like remains behind and is split up on neutralization with alkali, with formation of free pyridine and so forth. It may also be, however, that the dilute acid only incompletely binds the bases, and more particularly the higher boiling weaker bases, owing to hydrolytic fission. By treatment with hot water after the purification with dilute acid both the salts of the bases as well as the free bases are dissolved-out without the aromatic light oils undergoing any washing loss. Preferably the charge is heated to temperatures exceeding 30,

more particularly above 40 C. and over, and is washed, e. g. twice, with 5-7% water each time. This. treatment makes subsequent or more intensive employmentof acid, which on the one hand would bind the bases securely but on the other hand would; cause new washing loss, absolutely unnecessary,

Theyield of purified aromatic light oils produced; according tothe invention is considerably higher than in the case of the wasteful purification with'concentrated sulphuric acid previously employed. An aromatic light oil is obtained in,

high yield which is highly valuable from a drivingpoint of view and. is completely stable on storage.

This result is obtained by avoiding any use of stronger acid in a concentration of above in the entire purifying process and by the final driving-off of the aromatic light oils in the presence of an alkali at elevated temperatures, these temperatures corresponding to, or being higher.

than, the boiling temperatures of the constituents of the aromatic hydrocarbons under treatment.

What we claim is:

1. In a method of purifying and stabilizing.

aromatic light oils being obtained by high temperature coking of mineral coal and containing considerableamounts of unsaturated hydrocarbons capable of changing upon standingintodiscoloring and resinous products: converting. only part of said unsaturated hydrocarbons into sulphonic acids and esters by subjecting ;the oil to washing with diluted sulphuric acid of only approximately 60 B. concentration, and preserving the nonconverted unsaturated hydrocarbons by subsequently destroying and removing said sulphonic acids and esters and other resin producersby means of distilling the oil at elevated temperature in the presence of alkali.

2. In a method of purifying and stabilizing aromatic light oils being obtained by high temperature coking of mineral coal and containing considerable amounts. of unsaturated hydrocarbons capable of changing upon standing into discoloring and resinous products: converting part of said unsaturated hydrocarbons into sulphonic acids and esters by subjecting the oil to washing.

with diluted sulphuric acid of approximately 60 B. concentration, thereupon washing. the oil with hot ,water, and preserving the nonconverted unsaturated hydrocarbons by subsequently destroying said sulphonic acids and esters and other resin producers by means of treating the oil with alkali at elevated temperature, whereupon distillation is effected.

3. In a method of purifying and stabilizing aromatic light oils being obtained by high. temperature coking of mineral coal and containing considerable amounts of unsaturated. hydrocarbons capable of changing upon standing into discoloring and resinous products: converting part of said unsaturated hydrocarbons into sulphonic acids and esters by subjecting the oil to washing with diluted sulphuric acid of approximately 60 B. concentration, thereupon destroying said sulphonic acids and esters and other resin producers by treating the oil with alkali at elevated temperature corresponding to about the boiling temperature of the oil, whereupon distillation is efiected.

4. In a method of purifying and stabilizing aromatic light oils being obtained by high temperature coking of mineral coal and containing considerable amounts of unsaturated hydrocarbons capable of changing upon standing into discoloring' and resinous products: converting part of said unsaturated hydrocarbons into sulphonic acids and esters by subjecting the oil at temperatures above room temperature, up to about 40 C., to washing with diluted sulphuric acid of approximately 60 B. concentration, then washing the oil with hot water, andthereuponpreserving the nonconverted unsaturated hydrocarbons by destroying and removing said sulphonic acids and esters and other resin producers by means of treating and distilling the oil at elevated temperature in the presence of alkali.

ALFRED POTT. HANS BROCHE. KUNO EHRMANN. 

